RESUMO
3,4,9,10-Perylenetetracarboxylic-dianhydride (PTCDA) aggregates have unique optical properties and are model materials for studying exciton energy transfer (EET) in planar stacked molecular aggregates. In the framework of density matrix theory, a hierarchy of molecular transition operator expectation values could be constructed to derive the equations of motion of multi-exciton states. Realistic parameters for PTCDA molecules are used to study EET and the optical response of two-dimensional aggregates upon local excitation. Our simulations show that information about the dark state can be obtained with local field excitation and the inter-chain coupling results in a red-shift of the lowest excitonic energy level. Configuration effects, inter-chain detuning and multi-exciton states are discussed. The calculated lowest excitonic energy level of a 2D PTCDA aggregate is qualitatively consistent with the lowest experimental absorption peak of a PTCDA film. The obtained results are valuable for the study of aggregates in optical nanocavities and for the design of photoelectric devices.
RESUMO
The paper applies the event study method and econometric models to investigate the impacts of COVID-19 on China's green bond market for the first time. We find that (1) the COVID-19 pandemic has significant impacts on China's green bond market and increases the cumulative abnormal return (CAR) of the green bonds greatly. After the pandemic is relieved, the CAR drops significantly; (2) the improving of bond issuers' governance capacity, the weakening of information asymmetry and the reinforcing of debt-paying ability can effectively mitigate the negative impacts and positively promote the recovery of bond issuers after the pandemic; (3) the impacts of bond issuers' governance capacity, information asymmetry and debt-paying ability on the CAR of green bonds are significantly heterogeneous before and after the pandemic due to their property rights and whether they are listed or not.